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: 7: Respiratory System
Respiration
The body needs a continual supply of oxygen. One may survive for a long time without food, for less than a week without water, but one would not last more than a few minutes without oxygen. In addition, for a continual supply of oxygen, the body also needs some means of disposing of the waste carbon dioxide produced by the function of the body cells. The body also needs an efficient distribution system to deliver the oxygen to all 600 billion body cells and carry off their cabon dioxide. The word respiration is used to describe all the processes associated with the release of energy in the body. Breathing makes a continual replenishment of the oxygen in the lungs, drawing in fresh air from the atmosphere and expels the unwanted carbon-diooxide outside. Blood circulation delivers the oxygen and brings waste gases to the lungs. We have already discussed the circulatory system in the previous section. Here we shall discuss the anatomy and the functions of the respiratory system.
Organs of the System
The respiratory system includes passageways and tubes through which the air passes: the nose, pharynx, larynx, trachea, two bronchi, bronchioles, arranged in a sequence that branches and rebranches and look like an inverted tree. The tubes end in tiny air sacs called alveoli in which the exchange of gases takes place. The bronchioles and alveoli constitute the lungs. The system includes a bellows arrangement-the rib cage-operated by muscles (of which the diaphragm is especially important) and controlled by nerves.
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